I. Field of the Invention
This invention relates to new crosslinked sulfonated polymers of polystyrene and styrene copolymers and to a process for the production thereof. More particularly, the invention relates to a process for producing crosslinked sulfonated polystyrene or styrene copolymers employing selected crosslinking agents during the sulfonation reaction so as to achieve crosslinking and sulfonation of the polymer simultaneously and efficiently in a homogeneous system. The process yields crosslinked sulfonated styrene polymers undisclosed in the prior art.
II. Brief Description of the Prior Art
Prior art procedures for preparing crosslinked sulfonated polystyrene or styrene copolymers involve the sulfonation of polymers which have been previously crosslinked with difunctional reagents or which contain copolymerized alkenyl halides within the backbone of the polymer itself. The crosslinking may then be achieved during formation of the polymer as is the case when styrene divinyl aryl compounds are sulfonated. Typical of such methods is that described by Davankov et al. in German Offen. No. 2,045,096 (Chem. Abs. 75, 6841v). Alternatively, the styrene polymers may contain therein an alkenyl halide together with a Friedel-Crafts type catalyst, which, upon exposure to elevated temperatures during sulfonation, will effect crosslinking so as to produce the sulfonated crosslinked polymer. The latter method is described in U.S. Pat. No. 2,628,193.
The methods of the prior art thus, in all cases, require the presence of specific components within the backbone of the polymer thereby limiting the choice of molecular weight and final structure of the sulfonated polymer. Moreover, in cases wherein the polymer is crosslinked prior to sulfonation, the degree of crosslinking desired in the final polymer must be incorporated into the starting polystyrene copolymer. Often, however, a high crosslinking density is desired in the final product and this necessitates working with a styrene polymer which is insoluble in the sulfonation medium resulting in incomplete or partial sulfonation. Similarly, incomplete sulfonation is achieved when alkenyl halides or the like are incorporated into the polymer since the aromatic sites available for sulfonation are proportionately reduced.